Color picture tube utilizing a shadow mask which selects colors and detects the displacement of the beam

ABSTRACT

A color picture tube having a shadow mask which has, in addition to the function of selecting colors depending on the difference in incidence angles of a plurality of electron beams, a function of detecting the displacement of such electron beams. A signal thereby obtained is utilized so as to automatically correct vertical displacement and out-of-focussing of the electron beams thereby to increase the density of the electron beams impinging against the fluorescent screen and to improve the brightness and resolution of the picture obtained.

Enited States Patent lida [75] Inventor: Teiji Iida, Chiba-ken, Japan[73] Assignees: Hitachi, Ltd., Tokyo; Teiji llida,

Chiba-ken, Japan [22] Filed: June 25, 1969 [21] Appl. No.: 836,424

[30] Foreign Appilcation Priority Data June 28, 1968 Japan ..43/45337Oct. 24, 1968 Japan ..43/927l3 Oct. 24, 1968 Japan ...43/927l4 Nov. 11,1968 Japan ....43/81915 Jan. 20, 1969 Japan ..44/3935 Jan. 20, 1969Japan ..44/3936 Feb. 8, 1969 Japan ..44/9440 Mar. 14, 1969 Japan....44/19369 Mar. 14, 1969 Japan ...44/22806 Apr. 9, 1969 Japan...44/275l0 May 13, 1969 Japan ..44/36788 May 13, 1969 Japan ..44/36789[52] U.S. Cl. "SIS/$1 C, 313/85 S [58] Field of Search ..31S/21 C;313/85 S,

Primary ExaminerCarl D. Ouarforth Assistant Examiner-J. M. PotenzaAtt0rneyCraig, Antonelli and Hill [57] ABSTRACT A color picture tubehaving a shadow mask which has, in addition to the function of selectingcolors depending on the difference in incidence angles of a plurality ofelectron beams, a function of detecting the displacement of suchelectron beams. A signal thereby obtained is utilized so as toautomatically correct vertical displacement and out-of-focussing of theelectron beams thereby to increase the density of the electron beamsimpinging against the fluorescent screen and to improve the brightnessand resolution of the picture obtained.

24 Claims, 33 Drawing Figures PATENTEDMY Hm 373L134 SHEET 01 0F 14INVENTOR TEI J I II DA ATTORNEYS PATENTEDHAY' 1 I915 SHEET 02 OF 14 mEEFFEBW INVENTOR TEIJ'I I PA ATTORNEYS PATENTEDHAY 1191a 3,731,134

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ATTORNEYS PATENTEU H915 3.731.134

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ATTORNEYS INVENTOR r5111 I M ATTORNEYS PATENTED MY 1 I973 SHEET 07UF 14INVENTOR TEIJI IIDA ATTORNEYj PATENTEDMAY' Hm $731,134

SHEET 08 {1F 14 INVENTOR TEITI IIDA FIG I? BY Md ATTORNEYS PATENTEU11973 3.731.134

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SHEET 11 OF 14 DENSITY INVENTOR fPOl l PUI DI I UI QI PQI JIQMI DI IM IPUI QI l I 1,71 IIDA ATTORNEYS PATENTEU W 1 1975 SHEET 13 0F 14 INVENTORf/ZITI .IIDA

ATTORNEYS COLOR PICTURE TUBE UTKLIZING A SHADOW MASK WHECH SELECTSCOLORS AND DETECTS THE DISPLACEMENT OF THE BEAM BACKGROUND OF THEINVENTION 1. FIELD OF THE INVENTION This invention relates to colorpicture tubes and more particularly to a color picture tube in whichdisplacement of a plurality of electron beams is detected by a shadowmask disposed in front of a fluorescent screen so that the displacementcan automatically be corrected.

2. DESCRIPTlON OF THE PRIOR ART ln conventionally employed color picturetubes or shadow mask tubes, including those based on the Trinitronsystem of the SONY Corporation, the rate at which the electron beamspass through the shadow; mask, that is, the electron beam utility factoris quite low, i.e., of the order of percent to percent. Thus, thephosphors are caused to luminesce at a low rate by the electron beamsthat have passed through the shadow mask, resulting in a dark picture.It is therefore common practice to increase the anode voltage of thepicture tube so as to raise the speed of electron beams passing throughthe shadow mask thereby to cause the phosphors to luminesce at a higherrate. However, the impingement of the high-speed electron beams againstthe phosphors generates X-rays and it is not yet possible to obtain asufficiently bright picture even when the amount of X-rays so generatedbecomes as high as the allowable limit and might adversely affect thehuman body.

SUMMARY OF THE lNVENTlON It is a primary object of the present inventionto provide a color picture tube in which a shadow mask which isprimarily used for the selection of colors depending on the differencein incidence angles of a plurality of electron beams has also a functionof detecting a displacement of the electron beams and a signal therebyobtained is utilized so as to automatically correct verticaldisplacement and out-of-focussing of the electron beams thereby toincrease the density of electron beams impinging against the fluorescentscreen and to improve the brightness and resolution of the picture.

Another object of the present invention is to provide a color picturetube having such a shadow mask in which the electron beam passages arein the form of many slit-like openings arranged in the direction of beamscanning so as to improve the horizontal resolution and to control theextent of the beam directed to a phosphor among a plurality of phosphorswhich have a low luminous efficiency.

A further object of the present invention is to provide a color picturetube having such a shadow mask in which comb-shaped shadow mask sectionsare assembled tegether in such a manner that the ends of stripelectrodes of each of the shadow mask sections are connected through anelectrically insulating member to the base portion of the oppositeshadow mask section, and the shadow mask sections are electricallyinsulated from each other so that the strip electrodes can act as meansfor detecting any displacement of the electron beams from theirpredetermined path.

Another object of the present invention is to provide a color picturetube having such a shadow mask in which many horizontally arranged slitsare formed to serve as electron beam passages and a secondary electronemission layer is provided on each of the strips defining the slits fordetecting any displacement of the electron beams.

Yet another object of the present invention is to provide a colorpicture tube in which beams emitted from electron guns are modulated andan MgO layer or a combination of spaced MgO segments and a signal wireis provided on each strip of a shadow mask for detecting anydisplacement of the modulated beams, the detected signal being then fedback through a feedback system so as to automatically correct thedisplacement.

A further object of the present invention is to provide a color picturetube having such a shadow mask in which many slits for allowing thepassage of electron beams therethrough are formed in the horizontalscanning direction of the beams, and each strip defined between theadjacent slits is provided on its surface opposite to the electron gunsan upper electrode and a lower electrode which extend in thelongitudinal direction of the strip and are electrically insulated fromeach other as well as from the strip.

A yet a further object of the present invention is to provide a colorpicture tube having such a shadow mask which is disposed in front of afluorescent screen having phosphor strips arranged in the form ofhorizontal stripes, which has many beam passage slits arranged oppositeto the phosphor strips in a number substantially the same as the numberof effective scanning lines, and in which a first electrode and a secondelectrode, vertically separated from each other, are provided through anelectrical insulatorion an odd strip and an even strip of the shadowmask, respectively, for deriving a signal representing displacement ofthe electron beams.

A still further object of the present invention is to provide a colorpicture tube in which part of phosphor strips on a fluorescent screencan be used in common to both the odd field and the even field.

in accordance with the present invention, any displacement of aplurality of electron beams is detected by the shadow mask disposed infront of the fluorescent screen so as to automatically correct thedisplacement. Therefore, the electron beam utility factor can beincreased to several times that of conventional shadow masks or aperturegrills, thereby giving a very bright picture and a very satisfactoryresolution. Further, by virtue of the increased electron beam utilityfactor, a sufficient intensity can be obtained with an anode voltagesubstantially the same as that used for black-andwhite television,thereby facilitating transistorization of color television receivers.Moreover, owing to the fact that the shadow mask according to thepresent invention has many horizontally arranged slits for the passageof electron beams therethrough, horizontal scanning by the electronbeams is not in any way obstructed to ensure a satisfactory horizontalresolution. in the present invention, the electron gun for the redphosphor which has the lowest luminous efficiency among a number ofphosphors may have a horizontally oval shape so that the amount of beamimpinging against the red phosphor is larger than the amounts of beamsimpinging against other phosphors, thereby to improve the rate ofluminescence of the red color and to enhance the color improvement.Since the shadow mask detects any displacement and out-of-focussing of aplurality of electron beams, the time for detecting electron beamdisplacement can be remarkably shortened compared with that inconventional apple tubes and Andromeda tubes, thereby facilitatingfeedback control and simplifying the structure of the feedback circuit.

Other objects, features and advantages of the present invention will beapparent from the following detailed description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. I is a schematic perspective view of part of an embodiment of thecolor picture tube according to the present invention.

FIG. 2 is an enlarged vertical sectional side elevational view of partof a shadow mask and phosphors in the embodiment of the presentinvention shown in FIG. 1.

FIG. 3 is a back view of the shadow mask shown in FIG. 2.

FIG. 4 is an enlarged vertical sectional side elevational view of partof a shadow mask and phosphors in another embodiment of the presentinvention.

FIG. 5 is a back view of the shadow mask shown in FIG. 4.

FIG. 6 is an enlarged verticalsectional side elevational view of part ofa shadow mask and phosphors in a further embodiment of the presentinvention.

FIG. 7 is an enlarged vertical sectional side elevational view of partof a shadow mask and phosphors in a yet further embodiment of thepresent.

FIG. 8 is a block diagram of a control circuit for correcting thedeflected beams by a signal representing electron beam displacement in astill further embodiment of the present invention.

FIG. 9 is a back view of a shadow mask in the embodiment shown in FIG.8.

FIG. 10 is a schematic front elevational view of a shadow mask inanother embodiment of the present invention.

FIG. 11 is a front elevational view of a shadow mask section in theshadow mask shown in FIG. 10.

FIG. 12 is an enlarged vertical sectional side elevational view of partof a shadow mask and phosphors in still another embodiment of thepresent invention, showing means for detecting the arrival position ofthe electron beams.

FIG. 13 is a back view of the shadow mask shown in FIG. 12.

FIG. 14 is an enlarged back view of part of a shadow mask in yet anotherembodiment of the present invention.

FIG. I5 is an enlarged vertical sectional side elevational view of partof a shadow mask and phosphors in a further embodiment of the presentinvention, showing means for detecting any displacement of electronbeams.

FIG. 16 is a back view of the shadow mask shown in FIG. 15.

FIG. 17 is an enlarged back view of part ofa shadow mask in a yetfurther embodiment of the present invention.

FIG. 18 is an enlarged vertical sectional side elevational view of partof a shadow mask and phosphors in a still further embodiment of thepresent invention, showing means for detecting the arriving position ofelectron beams.

FIG. I9 is a back view of the shadow mask shown in FIG. 18.

FIG. 20 is an enlarged vertical sectional side elevational view of partof a shadow mask and phosphors in another embodiment of the presentinvention.

FIG. 21 is a back view of the shadow mask shown in FIG. 20.

FIG. 22 is an enlarged vertical sectional side elevational view of partof a shadow mask and phosphors in still another embodiment of thepresent invention.

FIG. 23 is a back view of the shadow mask shown in FIG. 22.

FIG. 24 is a schematic enlarged vertical sectional side elevational viewof part of a shadow mask and phosphors in yet another embodiment of thepresent invention.

FIG. 25 is a schematic enlarged vertical sectional side elevational viewof part of a shadow mask and phosphors in another embodiment of thepresent invention.

FIGS. 26 and 27 are graphic illustrations of the density distribution ofelectron beam spots with respect to the shadow mask of the presentinvention.

FIG. 28 is a schematic enlarged vertical sectional side elevational viewof part of a shadow mask and phosphors in a further embodiment of thepresent invention.

FIG. 29 is a back view of the shadow mask shown in FIG. 28.

FIG. 30 is a schematic view showing the state of beam scanning in theshadow mask shown in FIG. 28.

FIG. 31 is a schematic enlarged vertical sectional side elevational viewof a shadow mask in another embodiment of the present invention.

FIGS. 32a and 32b are schematic enlarged vertical sectional sideelevational views of part of a shadow mask and phosphors in aquadri-color picture tube embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 through 3,an embodiment of the color picture tube according to the presentinvention comprises three electron guns 1, 2 and 3 for red, green andblue which are lined up in a vertical direction at the neck portion of aglass bulb 4. Each of the electron guns 1, 2 and 3 is provided with acontrol grid, focussing electrodes and vertical deflecting electrodes.

The red, green and blue electron beams emitted from the respectiveelectron guns I, 2 and 3 impinge against a fluorescent screen 5 which isformed by horizontally coating sets of red-, greenand blue-emittingphosphor strips G, R and B. The number of sets of the phosphor strips G,R and B is 490 or equal to the number of effective horizontal scanninglines. A shadow mask 6 is disposed opposite to the fluorescent screen 5with a predetermined spacing defined therebetween. The shadow mask 6 isprovided with horizontally running slits 7 for passage therethrough ofthe electron beams at positions opposite to the sets of the phosphorstrips.

The width of each slit 7 is equal to one-third of the spacing betweenthe scanning lines and the total number of the slits 7 is equal to thenumber of effective scanning lines or 490. In order to increase themechanical strength of the shadow mask 6, strips 7 defining the slits 7therebetween are connected to each other at a plurality of portions. Thesurface of the shadow mask 6 opposite to the electron guns is entirelycovered by an electrically insulating layer 8 applied as a coating, anda metal layer for detecting vertical displacement and outof-focussing ofthe electron beams is formed on the insulating layer portion 8 coveringeach strip 7'. The odd metal layers are designated as first electrodes9a, while the even metal layers are designated as second electrodes 9b.The first electrodes 9a are connected to a common signal lead 10 whilethe second electrodes 9b are connected to a common signal lead 11, sothat, when the electron beams impinge against any one of the firstelectrodes 9a and second electrodes 9b, a signal is delivered througheither lead for detecting vertical displacement and out-of-focussing ofthe electron beams.

Referring to FIGS. 4 and 5, another embodiment of the present inventioncomprises a shadow mask 6' disposed opposite to a fluorescent screen 4having many sets of red-, greenand blue-emitting phosphor strips, R, Gand B extending in a horizontal direction. The shadow mask 6' isprovided with horizontally running slits 7a for passage therethrough ofthe electron beams at positions opposite to the sets of the phosphorstrips as in the case of FIG. 2. The width of each slit 7a is equal toone-third of the spacing between the scanning lines and the total numberof the slits 7a is equal to the number of effective scanning lines or490. Each of the slits 7a is defined between adjacent strips 70'. Eachof the odd strips 70' is provided on its surface opposite to theelectron guns with 526 segments of MgO 7b which have a fixed width andare spaced at a fixed distance apart from each other in the longitudinaldirection of the strip 70' to form segments of a predetermined pitch.Each of the even'strips 7a is provided on its surface opposite to theelectron guns with 789 segments of MgO 70 which have a fixed width andare spaced at a fixed distance apart from each other in the longitudinaldirection of the strip 7a to form segments having a pitch different fromthe segments on each of the odd strips. It will be noted that the numberof the MgO segments 7c is 1.5 times that of the Mg() segments 712. Aconductor wire 7e runs longitudinally above the series of the MgOsegments 7b on the odd strip 7a with an electrically insulating support7d interposed therebetween, while a conductor wire 7f runslongitudinally above the series of the MgO segments 7e on the even strip7a with an electrically insulating support 7d interposed therebetween.The ends of the conductor wires 7e and 7f are connected to a commonexternal lead 73 and the potential of the conductor wires 7e and 7f iskept at a higher value than that of the shadow mask 6'. Thus, when thehorizontally scanning electron beams are displaced from the slit 7a toimpinge against the MgO segments and secondary electrons are therebyemitted, the secondary electrons are arrested by the conductor wire 7eor 7f to derive the electron beam displacement in the form of afrequency.

When, during horizontal scanning with the electron beams, the beamsimpinge against the MgO segments 7b whose number is 526, a frequency of9.6 megacycles due to the stream of secondary electrons is derived fromthe conductor wire 7e, while a frequency of 14.4 megacycles is derivedfrom the conductor wire 7f when the beams impinge against the MgOsegments 7c whose number is 789.

FIG. 6 shows an improvement in the shadow mask structure shown in FIG.2. In the shadow mask 6 shown in FIG. 6, a grid 6a for absorbingsecondary electrons emitted by the impingement of electron beams isprovided on each of the first and second electrodes 9a and 9b through anelectrical insulator 6b so as to prevent any undesirable color blur andreduction in the color purity due to the arrival of secondary electronsat the fluorescent screen.

In a further embodiment shown in FIG. 7 showing a modification of thestructure shown in FIG. 6, a secondary electron absorbing grid isadditionally provided through an electrical insulator 6d on each of thestrip 7 at the surface opposite to the fluorescent screen 5 so as toabsorb secondary electrons emitted from the aluminum metal back MBprovided on the tri-color fluorescent screen 5 thereby to preventundesirable color blur and reduction in the color purity. Thisarrangement is very important in a system adopted for the subsequentacceleration and focussing of electron beams.

Referring to FIG. 8, there is shown a block diagram of a feedbackcircuit for the detection of the arriving position of electron beams.The circuit is used in combination with the shadow mask of the kinddescribed hereinabove so that the electron beam displacement signaldetected by the shadow mask can be fed back to the beam control systemfor the electron guns to automatically correct the arrival position ofthe electron beams. Three pilot carrier oscillators 19, 20 and 21deliver three different pilot carrier signals at respective frequenciesf f and f which are higher than 4.8 megacycles so as not to interferewith satisfactory television reception. The three pilot carrier signalsare applied together with a picture signal from a television receiver 22to the control grids of the electron guns 1, 2 and 3 through red, greenand blue mixers 23, 24 and 25, respectively, to modulate the electronbeams from the electron guns 1, 2 and 3. The modulated electron beamsscan along the slits 7 of the shadow mask 6. A modulated beam deflectioncontrol circuit 27 applies a deflecting voltage to the verticaldeflecting electrodes of the respective electron guns 1, 2 and 3 so asto forcedly deflect the modulated beams toward, for example, the upperedge of the slit 7 of the shadow mask 6, and thus the modulated beamsimpinge against the strip 7 of the shadow mask 6.

When the modulated beams deflected by the control circuit 27 impingeagainst the upper or lower edge of the slit 7 of the shadow mask 6, asignal including the frequency components f,, f, and f; of the threepilot carrier signals corresponding to the impinged beams is derivedfrom the shadow mask 6, and the signal is amplified by an amplifier 28which is connected to the shadow mask 6 through a capacitor C. Thesignal output from the amplifier 28 is separated by red, green and blueband-pass filters 29, 30 and 31, and the signals delivered from thefilters 29, 30 and 31 are applied to red, green and blue detectors 32,33 and 34, respectively, to be demodulated by the latter. Thedemodulated reproduced signals are applied to red, green and bluevertical deflecting amplifiers 35, 36 and 37, respectively, to operatethe latter. The output signals from the amplifiers 35, 36 and 37 arethen applied to the vertical deflecting electrodes for the electron guns1, 2 and 3 for further suppressing the upward deflection of the electronbeams. Thus, any further deflection of the electron beams by themodulated beam deflection control circuit 27 can be prevented. Such anoperation is repeated each time the electron beams impinge against theshadow mask 6 by being deflected by the deflecting voltage supplied fromthe control circuit 27. Therefore, the locus of the beams will be asshown by the broken line in FIG. 9.

Even if vertical displacement of the beams tends to develop in the aboveoperation, that is, when the beams tend to be displaced toward the loweredge of the slit 7 of the shadow mask 6 for some reason, downwarddisplacement of the beams would not occur since the beams are forcedlydeflected toward the upper edge of the slit 7 by the control circuit 27.

On the other hand, when the beams tend to be further displaced towardthe upper edge of the slit 7, this displacement is combined with theforced deflecting action on the electron beams with the result that theelectron beams are deflected to an excessive degree and impinge againstthe upper edge of the slit 7 at a rapid rate. However, impingement ofthe electron beams results in detection of frequency components includedtherein and the control feedback system is immediately operated tosuppress deflection by the control circuit 27. Therefore, the beams arepulled back toward the lower edge of the slit 7. The locus of beamsrunning in the slit 7 does not take a periodic waveform as shown in FIG.9 but assumes an irregular waveform.

Another embodiment of the present invention includes a shadow mask 45 asshown in FIGS. 10 and 11. The shadow mask 45 consists of a pair ofcomb-shaped shadow mask sections 41 of structure as seen in FIG. 11.Each shadow mask section 41 is provided with (n 1/2) elongated stripelectrodes 42 the width of which is equal to or larger than the spacingbetween scanning lines. (n represents the number of effective scanninglines.) The strip electrodes 42 of the shadow mask section 41 areparallelly spaced from each other at a distance of, for example, 2dwhich is two times the width d of each strip electrode 42. The shadowmask sections 41 are combined together in a flat fashion in such amanner that any one of the strip electrodes 42 of each shadow masksection 41 extends into the space defined between the adjacent stripelectrodes 42 of the opposite shadow mask section 41, and the ends ofthe strip electrodes 42 of each shadow mask section 41 are connectedthrough electrically insulating members 43 to the base portion A of theopposite shadow mask section 41, thereby defining electron beam passageslits 44 between the strip electrodes 42 so interlaced.

The shadow mask 45 constructed in the above manner is secured oppositeto a fluorescent screen formed by arranging red-, greenand blue-emittingphosphor strips R, G and B in a horizontally striped pattern on the frominner wall face of a glass bulb so that the slits 44 run horizontally infront of the fluorescent screen. The strip electrodes 42 of the shadowmask sections 41 constituting the shadow mask 45 are operated aselectrodes for deriving a beam displacement signal which, when detected,is fed back to an electron beam control circuit through a feadbacksystem so as to correct displacement of electron beams and to improvethe picture brightness and resolution.

While, in the present embodiment, the width of the strip electrodes 42and the spacing between the strip electrodes 42 have been specified, theshadow mask according to the present invention is in no way limited tosuch specific values and many changes may be made therein as required.Further, as a means for preventing mechanical vibration of the strips ofthe shadow mask, suitable strips or narrow band-like members may bebonded or secured to one or both faces of the shadow mask in such arelationship that they cross perpendicularly with respect to the stripof the shadow mask.

Referring to FIGS. 12 and 13 showing another embodiment of the presentinvention, the color picture tube includes a fluorescent screen 51 whichis formed by horizontally coating sets of red-, greenand blueemittingphosphor strips R, G and B. The number of sets of the phosphor strips is480 or equal to the number of effective scanning lines. A shadow mask 52is disposed opposite to the fluorescent screen 51 with a predeterminedspacing defined therebetween. The shadow mask 52 is provided withhorizontally running slits 53 for passage therethrough of electron beamsat positions opposite to the sets of the phosphor strips. The width ofeach slit 53 is equal'to one-third of the spacing between the scanninglines and the total number of slits 53 is equal to the number ofeffective scanning lines or 480. In order to increase the mechanicalstrength of the shadow mask 52, strips 53 defining the slits 53therebetween are connected to each other at a plurality of portions byconnecting members 53". Each of the odd strips 53 is provided on itssurface opposite to the electron guns with 526 segments of secondaryelectron emitting Mg0 54a which have a fixed width and are spaced apartat a fixed distance from each other in the longitudinal direction of thestrip 53. Each of the even strips 53' is provided on its surfaceopposite to the electron guns with 789 segments of secondary electronemitting Mg0 54b which have a fixed width and are spaced apart at afixed distance from each other in the longitudinal direction of thestrip 53'. It will be noted that the number of the Mg0 segments 54b is1.5 times that of the Mg0 segments 54a. A signal wire 56a runslongitudinally above the series of the Mg0 segments 54a on the odd strip53 with an electrically insulating support 55a interposed therebetween,while a signal wire 56b runs longitudinally above the series of the Mg0segments 54b on the even strip53' with an electrically insulatingsupport 55b interposed therebetween. The ends of the signal wires 56aand 56b are connected to a common signal lead 57 and the potential ofthe signal wires 56a and 56b is kept at a higher value than that of theshadow mask 52. Thus, when the electron beams impinge against the Mg0segments and the secondary electrons are thereby emitted, the secondaryelectrons are absorbed by the signal wires 56a and 56b to derive theelectron beam displacement in the form of a frequency,

and at the same time, to derive a pilot carrier signal contained in thesecondary electrons.

When beam displacement takes place during scanning with the electronbeams and the beams impinge against the Mg segments 54a whose number is526, a frequency of 9.6 megacycles, due to the stream of secondaryelectrons, is derived from the signal wire 56a, while a frequency of14.4 megacycles due to the stream of secondary electrons is derived fromthe signal wire 5612 when the beams impinge against the Mg0 segments5412. None of these frequencies interferes with the video signal.

In a further embodiment of the present invention shown in FIG. 14, thereis shown a shadow mask 52 which is similar in construction to that shownin FIGS.

12 and 13. The surface of each strip 53 opposite to the electron guns isseparated into an upper portion and a lower portion along thelongitudinal direction of the strip 53. The upper portion is coated with789 segments of Mg0 63a which have a fixed width and are spaced apartfrom each other in the longitudinal direction of the strip 53', whilethe lower portion is provided with 526 segments of Mg0 63b which have afixed width and are spaced apart at a fixed distance from each other inthe longitudinal direction of the strip 53'. Centrally to each strip 53'and opposite to the electron guns, a signal wire 64, supported by anelectrically insulated support, extends in the longitudinal direction ofthe strip 53'. The signal wires 64 are connected to a common signal lead65 which is connected to bandpass filters (not shown) for three colorpilot carriers in a feedback circuit (not shown). This arrangement caneliminate polarity switch-over circuits. Vertical displacement ofelectron beams can thus be detected by the Mg0 segments 63a and 63bprovided for the specific purpose.

In the embodiment described above, a potential difference may beestablished between the fluorescent screeen and the shadow mask asrequired so as to further accelerate andfocus the electron beams passedthrough the slits of the shadow mask, thereby avoiding blurring of thecolor.

Referring to FIGS. and 16 showing a yet further embodiment of thepresent invention, there is shown a fluorescent screen 71 which isformed by horizontally coating sets of red-, greenand blue-emittingphosphor strips R, G and B in horizontally striped pattern. The numberof sets of the phosphor strips is 480 or equal to the number ofeffective scanning lines. A shadow mask 72 is disposed opposite to thefluorescent screen 71 with a predetermined spacing defined therebetween.The shadow mask 72 is provided with horizontally running slits 73 forthe passage therethrough of electron beams at positions opposite to thesets of the phosphor strips; The width of each slit 73 is equal toone-third of the spacing between the scanning lines and the total numberof the slits 73 is equal to the number of effective scanning lines or480. In order to increase the mechanical strength of the shadow mask 72,strips 74a and 74b defining the slits 73 therebetween are connected toeach other at a plurality of portions by connecting members 74. Each ofthe odd strips 74a is provided on the surface opposite to the electronguns with 526 secondary electron emitting segments 75a of material suchas tin or carbon which emits less secondary electrons than the material,steel, of the shadow mask 72. The segments 750 have a fixed width andare spaced apart at a fixed distance from each other in the longitudinaldirection of the strip 74a. Similarly, each of the even strips 74b isprovided on the surface opposite to the electron guns with 7 89secondary electron emitting segments b of material such as tin orcarbon. The segments 75!; have a fixed width and are spaced apart at afixed distance from each other in the longitudinal direction of thestrip 7412. It will be noted that the number of the segments 75b is 1.5times that of the segments 75a. The strips 74a and 74b, hence the shadowmask 72 itself serves as a signal delivering electrode and a lead 76 isconnected to the shadow mask 72 for deriving a frequency due to thestream of secondary electrons emitted as a result of impingement ofelectron beams against the strips and for deriving a pilot carriersignal contained in the electron beams.

A shadow mask 72 shown in FIG. 17 has a structure similar to that shownin FIGS. 15 and 16. The surface of each of strips 74a and 74b isseparated into an upper portion and a lower portion along thelongitudinal direction of the strip. The upper portion is coated with789 secondary electron emitting segments 82a of material such as tin orcarbon. The segments 82a have a fixed width and are spaced apart at afixed distance from each other in the longitudinal direction of thestrip. Similarly, the lower portion is coated with 526 secondaryelectron emitting segments 82b of material such as tin or carbon. Thesegments 82b have a fixed width and are spaced apart at a fixed distancefrom each other in the longitudinal direction of the strip. The shadowmask 72 itself serving as a signal delivering electrode is connected toa lead 83 which is connected to band-pass filters (not shown) for threecolor pilot carrier signals. This arrangement can eliminate polarityswitch-over circuits. Vertical displcement of electron beams can thus bedetected by the secondary electron emitting segments 82a and 8212provided for the specific purpose.

Referring to FIGS. 18 through 21 showing other embodiments of thepresent invention, a fluorescent screen 91, a shadow mask 92, electronbeam passage slits 93, and strips 93 defining therebetween the slits 93and connected to each other at a plurality of portions by connectingmembers 93" have a'structure similar to that of the precedingembodiments.

In FIGS. 18 and 19, each strip 93' of the shadow mask 92 is provided onthe surface opposite to the electron guns with a layer of secondaryelectron emitting Mg0 94 for detecting the vertical displacement andout-of-focussing of electron beams. Centrally to the strip 93 andopposite to the Mg0 layer 94, a signal wire 95, supported by anelectrically insulating support 96, extends above-the Mg0 layer 94 inthe longitudinal direction of the strip 93'. The signal wires 95corresponding to the odd strips 93' are connected to a common signallead 97, while the signal wires 95 corresponding to the even strips 93'are connected to a common signal lead 98. These signal wires 95 areapplied with a potential higher than that applied to the shadow mask 92.Thus, the signal wire 95 absorb the secondary electrons emitted as aresult of the impingement of electron beams against the Mg0 layer 94 toderive a displacement signal contained therein thereby

1. A color picture tube comprising means for emitting a plurality ofelectron beams, a fluorescent screen formed by arranging sets ofphosphor strips of a plurality of colors in the horizontal scanningdirection of the electron beams in the same number as that of theeffective scanning lines, and a shadow mask provided with electron beampassage slits defined between strips, said slits being arranged in thehorizontal scanning direction of the electron beams at positionsopposite to said sets of phosphor strips, said shadow mask serving as ameans for detecting the vertical deflection of the electron beams withrespect to the scanning Direction thereof.
 2. A color picture tube asclaimed in claim 1, in which said shadow mask is provided with a controlcircuit for deflecting said electron beams toward one of the lower andupper edges of said slit.
 3. A color picture tube as claimed in claim 1,in which the odd strips of said shadow mask are electrically connectedtogether to constitute a first electrode group while the even strips ofsaid shadow mask are also electrically connected together to constitutea second electrode group, and said first and second electrode groups areelectrically insulated from each other so as to detect displacement ofthe electron beams.
 4. A color picture tube as claimed in claim 3, inwhich said electron beams are modulated by respective pilot carriers ofdifferent frequencies and the pilot carrier signals are derived fromsaid electrode groups to detect displacement of the electron beams.
 5. Acolor picture tube as claimed in claim 3, in which said electron beamsare modulated by a common pilot carrier.
 6. A color picture tube asclaimed in claim 3, in which a grid for absorbing secondary electrons isdisposed on at least one of the surfaces of each said strip of saidshadow mask.
 7. A color picture tube as claimed in claim 1, in whicheach of the odd strips and each of the even strips of said shadow maskare provided on the surface opposite to said electron beam emittingmeans with secondary electron emitting segments of different pitches,respectively.
 8. A color picture tube as claimed in claim 7, in which asignal wire for absorbing secondary electrons extends in thelongitudinal direction of each said strip over the surface which isprovided with said secondary electron emitting segments, said signalwires being connected to a common signal lead.
 9. A color picture tubeas claimed in claim 1, in which each said strip is provided with anupper series and a lower series of secondary electron emitting segmentsof different pitches arranged in the longitudinal direction of saidstrip.
 10. A color picture tube as claimed in claim 9, in which a signalwire for absorbing secondary electrons extends in the longitudinaldirection of each said strip over the surface which is provided withsaid secondary electron emitting segments, said signal wires beingconnected to a common signal lead.
 11. A color picture tube as claimedin claim 1, in which a layer for emitting secondary electrons isdeposited on the surface of said shadow mask opposite to said electronbeam emitting means, and a signal wire for absorbing secondary electronsextends in the longitudinal direction of each said strip over thesurface which is provided with said secondary electron emitting layer,the odd signal wires being connected to a common signal lead while theeven signal leads being connected to another common signal lead.
 12. Acolor picture tube as claimed in claim 1, in which each said strip isprovided with a pair of separate electrodes arranged on the upper andlower portions of the strip for detecting the deflection of electronbeams, respectively.
 13. A color picture tube comprising means foremitting a plurality of electron beams, a fluorescent screen formed byarranging sets of phosphor strips of a plurality of phosphors, in afixed pattern so that the suitable phosphors among the set of phosphorscan be used in common to both the odd field and the even field, eachphosphor strip in said sets of phosphor strips having a width which isone-half of the spacing between the scanning lines, and a shadow maskdisposed opposite to said fluorescent screen and provided with electronbeam passage slits defined between strips, said slits being arranged inthe horizontal scanning direction of the electron beams in the samenumber as that of effective scanning lines and having a width which isone-half of the spacing between the scanning lines, said shadow maskserving as a means for detecting the position of the electron beams. 14.A color picture tube as claimed in claim 13, in which said shadow maskis provided with a control circuit for deflecting said electron beamstoward one of the lower and upper edges of said slit.
 15. A colorpicture tube as claimed in claim 13, in which the odd strips of saidshadow mask are electrically connected together to constitute a firstelectrode group while the even strips of said shadow mask are alsoelectrically connected together to constitute a second electrode group,and said first and second electrode groups are electrically insulatedfrom each other so as to detect displacement of the electron beams. 16.A color picture tube as claimed in claim 15, in which said electronbeams are modulated by respective pilot carriers of differentfrequencies and the pilot carrier signals are derived from saidelectrode groups to detect displacement of the electron beams.
 17. Acolor picture tube as claimed in claim 15, in which said electron beamsare modulated by a common pilot carrier.
 18. A color picture tube asclaimed in claim 15, in which a grid for absorbing secondary electronsis disposed on at least one of the surfaces of each said strip of saidshadow mask.
 19. A color picture tube as claimed in claim 13, in whicheach of the odd strips and each of the even strips of said shadow maskare provided on the surface opposite to said electron beam emittingmeans with secondary electron emitting segments of different pitches,respectively.
 20. A color picture tube as claimed in claim 19, in whicha signal wire for absorbing secondary electrons extends in thelongitudinal direction of each said strip over the surface which isprovided with said secondary electron emitting segments, said signalwires being connected to a common signal lead.
 21. A color picture tubeas claimed in claim 13, in which each said strip is provided with anupper series and a lower series of secondary electron emitting segmentsof different pitches arranged in the longitudinal direction of saidstrip.
 22. A color picture tube as claimed in claim 21, in which asignal wire for absorbing secondary electrons extends in thelongitudinal direction of each said strip over the surface which isprovided with said secondary electron emitting segments, said signalwires being connected to a common signal lead.
 23. A color picture tubeas claimed in claim 13, in which a layer for emitting secondaryelectrons is deposited on the surface of said shadow mask opposite tosaid electron beam emitting means, and a signal wire for absorbingsecondary electrons extends in the longitudinal direction of each saidstrip over the surface which is provided with said secondary electronemitting layer, the odd signal wires being connected to a common signallead while the even signal wires being connected to another commonsignal lead.
 24. A color picture tube as claimed in claim 13, in whicheach said strip is provided with a pair of separate electrodes arrangedon the upper and lower portions of the strip for detecting thedeflection of electron beams, respectively.